The present invention relates to metal forming dies and the like, and in particular to a two-piece guide pin and associated method.
Metal forming dies, such as stamping dies and the like, are well known in the art. Progressive metal forming dies are unique, very sophisticated mechanisms which have multiple stations or progressions that are aligned longitudinally, and are designed to perform a specified operation at each station in a predetermined sequence to create a finished metal part. Progressive stamping dies are capable of forming complex metal parts at very high speeds, so as to minimize manufacturing costs.
Heretofore, the dies used in metal forming presses have typically been individually designed, one-of-a-kind assemblies for a particular part, with each of the various components being handcrafted and custom mounted or fitted in an associated die set, which is in turn positioned in a stamping press. Not only are the punches and the other forming tools in the die set individually designed and constructed, but the other parts of the die set, such as stock lifters, guides, end caps and keepers, cam returns, etc., are also custom designed, and installed in the die set. Current die making processes require carefully machined, precision holes and recesses in the die set for mounting the individual components, such that the same are quite labor intensive, and require substantial lead time to make, test and set up in a stamping press. Consequently, such metal forming dies are very expensive to design, manufacture and repair or modify.
FIGS. 4 and 5 illustrate a prior art metal forming die that includes a die shoe 1 and a die pad 2, which are interconnected for mutual reciprocation by a plurality of spools 3. A spring mechanism 4 is mounted between die shoe 1 and die pad 2, and resiliently urges die pad 2 to a fully extended position. A metal forming die 5 is mounted on the outer surface of die pad 2. Each of the spools 3 includes an enlarged head 6 which reciprocates in an associated counter bore 7 in the bottom of die shoe 1. The heads 6 of spools 3 engage the top of the associated counter bores 7 to positively retain die pad 2 in its fully extended position. The other ends 8 of spools 3 are attached to the corners of die pad 2. While such constructions have been generally successful, they do not precisely control reciprocation between die pad 2 and die shoe 1, particularly in high speed, progressive die applications.
FIGS. 6 and 7 illustrate another prior art configuration, wherein pressed in pins 10, with locator bushings 11, have been added to the spools 3 shown in FIG. 1 to more precisely control the reciprocation between die pad 2 and die shoe 1.
FIGS. 8 and 9 illustrate yet another prior art configuration, which includes guide pins 10 and bushings 11, but substitutes footed keepers 13 and 14 for the common spools 3 to positively limit the reciprocation between die pad 2 and die shoe 1. More specifically, footed keepers 13 are mounted to die pad 2, and engage mating footed keepers 14 which are mounted on die shoe 1.
FIGS. 45-49 illustrate a prior art, integrally formed, one-piece guide pin 180 and associated method, which is somewhat similar to previously described guide pin 32, insofar as it has a generally cylindrical shaped body portion 181, with an alignment member 182 formed integrally at one end of guide pin body 181, and an enlarged head 183 formed integrally at the opposite end of guide pin body 181. As best illustrated in FIGS. 46-49, one-piece guide pin 180 is integrally formed from a solid bar 184 of hardenable steel having a cylindrical shape with an oversized outside diameter that is substantially commensurate with the outside diameter of the enlarged head 183. The cut length of the oversized bar 184 is determined in accordance with the desired height of the one-piece guide pin 180. The cut length of oversized bar stock 184 is precision machined, as shown in FIG. 47, to create the integral body 181 and head 183. Since the guide pin body reciprocates in an associated die bore for precisely guiding reciprocal motion between an associated die pad and die shoe, the exterior surface thereof must be hard and very accurate in shape and size to achieve the necessary low friction bearing and precision guide functions. The alignment member 182 is formed on that end of the one-piece guide pin 180 disposed opposite integrally formed head 183. Next, the precision machined guide pin 180 must be heat treated through nitride hardening or the like, as shown in FIG. 48. Because the nitride hardening process roughens the outside surface of the one-piece guide pin 180, at least the body portion 181 thereof must then be individually polished to facilitate close reception and sliding reciprocation in the associated die member bore. While one-piece guide pin 180 and the associated method are generally effective, the same are complicated and rather expensive. More specifically, the machining of the oversized bar material 184 requires holding a very tight tolerance on the machined guide pin body diameter. Substantial waste of material is also experienced during the machining process, since the guide pin 181 is typically much longer than the guide pin head 183. The formed part then needs to be transported to a specialty processor to be nitrated or the like to harden the outer surface of the guide pin body 181. The nitride process leaves a gray film on the entire surface of the guide pin 180, which requires a secondary polishing process by hand or otherwise. As a result, the lead time needed to produce one-piece guide pin 180 is relatively high, because of the heat treatment process after the part is machined, thereby requiring retailers to inventory substantial quantities of differently sized guide pins to meet customer demands. Furthermore, the required hand polishing adds significant time and cost to the manufacture of the one-piece guide pin 180. Hence, a guide pin construction and associated method which simplify the manufacturing process, reduce lead time and inventories, and reduce costs, as well as improve performance, would clearly be advantageous.